Silver halide color photographic materials are generally processed with a bleaching solution, etc. after color development. With an increase in the processing of the photographic materials in miniature shop laboratories, there has been an increased demand for rapid processing in recent years. The development of a rapid technique for the bleaching stage has been investigated to meet this demand.
Typical techniques include methods wherein an oxidizing agent having an oxidation-reduction potential of not lower than 150 mV at a pH of 6 such as the iron(III) complex salt of 1,3-diamino-propanetetraacetic acid is used in combination with an acid having a pKa of 2 to 5 in an amount of at least 1.2 mol/l, or a nitrate in an amount of at least 0.5 mol/l. In this manner, rapid bleaching is achieved while preventing bleach fog or preventing an increase in stain during storage after processing as disclosed in JP-A-2-282740 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-2-282741, JP-A-3-33847, and European Patent 427,204A.
It is noted that in each of the above-described patent specifications, an acid having a pKa of 2 to 5 is preferably used in an amount of at least 1.2 mol/l in order to prevent bleach fog.
Furthermore, the above-described patent specifications disclose that when the concentration of the iron(III) complex salt of an aminopolycarboxylic acid having an oxidation-reduction potential of not lower than 150 mV is less than 0.1 mol/l, bleaching is rapidly retarded. Hence it is preferred that the iron(III) complex salt is used in an an amount of not less than 0.1 mol/l, and the iron(III) complex salt is preferably used in the form of an ammonium salt to promote rapid bleaching.
For this reason, the iron(III) complex salt is used in the form of an ammonium salt in the bleaching solutions in the examples of the above described patent specifications. Particularly, ammonium 1,3-diamino-propanetetraacetato ferrate (ammonium 1,3-propylenediaminetetraacetato ferrate) is exemplified. In addition thereto, ammonium bromide, ammonium nitrate, ammonium thiosulfate, ammonium sulfite and ammonium water are formed, and the combined concentration of ammonium ion is at least 1.5 mol/l.
The present inventors have studied the above-described methods and have found that these methods are disadvantageous in the following three aspects.
A first problem is that in light-sensitive materials processed with the methods described above, the fastness of yellow dyes to light is reduced. The present inventors have experimentally found that fastness to light of fluorescent lamps is remarkably poor in comparison with light-sensitive materials processed with conventional methods requiring a long time of period using bleaching agents having an oxidation-reduction potential of not higher than 150 mV.
A second problem is that the bleaching solution travels upwardly along the inner walls of the tank in a processor containing the bleaching solution, and a large amount of a crystal is deposited on the surface or edges of the walls of the tank. The present inventors have found that the deposited crystal when brought into contact with the light-sensitive material during processing damages the light-sensitive material. Furthermore, the deposited crystal damages the smooth driving of the component parts of the processor and stains the processor, thereby increasing required maintenance for cleaning of the processor.
A third problem is that such bleaching solutions are highly corrosive to metals.
The processors are typically fabricated of metallic parts, which metallic parts are employed in various portions of the processor. Generally, stainless steel SUS316 is used for parts, which are brought into contact with the processing solution, taking resistance to corrosion of the stainless steel into consideration. However, the present inventors have found that the bleaching solutions described above corrode the parts in a short period of time, and stainless steel tanks, racks and roller shafts became damaged. Parts made of titanium are advantageously used with such bleaching solutions. However, titanous parts are expensive.